My first step towards Salt, the compelling new solo show from Leeds-based artist Selina Thompson, is wrong-footed. Miscommunication has the friend I'm going to see it with thinking it's on at Tobacco Factory, so we decide to drive. But it's on at Arnolfini. In the centre of Bristol. At 6.30pm. On a sunny Friday.

Needless to say we arrive late.

As we stumble blindly through the stalls, Thompson is already on stage wearing safety goggles and a white colonial-era dress, smashing away at a lump of, what is presumably, salt.

I got a free ticket to review the show. As we sit down I can't help but think, Shit.

But then Thompson starts talking again and my fleeting panic about what we may have missed dissolves.

The woman is incredible. Only a month since the experience(s) upon which Salt is based, here she is bold as blue sky, on a stage, telling the world what happened to her. What has always happened to her.

So what did happen to her, exactly? Well, in partnership with another artist she retraced a well-sailed route of the Transatlantic Slave Triangle, from the UK to Ghana to Jamaica and back again.

She sets out to journey deep into the past in order to understand some things that are at once intangible and very, very real.

Racism. Diaspora. Grief. The unresolved shame of many nations. There are some pretty heavyweight themes running through this work. Thompson is nothing if not ambitious.

She begins to lay out the pieces from the once-whole lump of salt. Each piece is slightly bigger than the last and represents both the characters on the ship of the first leg of her journey (described by Thompson as a "quiet trauma") and a centuries-old chain of which she, a dark-skinned black woman, forms the weakest, smallest link. A chain in which she, a dark-skinned black woman born in another time and place, would have been tied and beaten and raped and drowned.

That may sound hyperbolic. It is not. Some of the stories Thompson carries back with her, the insults she endured, the way she was made to feel as a direct consequence of her blackness, may sound (if you are not black) like they're from another time. But, shamefully, that simply isn't true.

There is a rawness to the work, in every sense of the word. Over a post-show drink another friend says she felt it wasn't fully formed. More of a sapling than a tree. She certainly has a point.

As a piece of theatre is does feel a little raw, undercooked. Thompson's words are strong and firmly glue the piece together but the way those words manifest on stage does feel like a work in progress. It would be interesting to see again in six or so months time.

It is also, of course, emotionally raw. Thompson is at times breathless not just from the effort of repeatedly taking a sledgehammer to salt (there is more to the show than this by the way) but the weight of it all too. The sheer, physical weight of a lifetime of racism and a centuries-old system which is not gone but all too easily forgotten.

And ultimately it's the rawness of her emotion that makes this work so impressive. Her vulnerability is a weapon and a shield. She stands alone, boldly claiming a space in a world that would – as her journey at times brings into painfully sharp relief – have her disappear.

She peels back her skin and says, Here. Look. This is how my insides are.

That takes courage of the highest order. And what is art if not the junction at the crossroads of courage and vulnerability?

Despite any theatrical polish she may yet apply, Thompson's show is unforgettable.